The easy-to-hard effect in perceptual learning shows that training with easier examples can facilitate initially difficult or impossible distinctions between very similar stimuli. This effect has been reported in humans and other species. We tested whether easy-to-hard training could facilitate visual discrimination in common goldfish (Carassius auratus). Fish (n = 6) performed a two-alternative forced choice discrimination task, which consisted of simultaneously presenting two striped patterns at a constant distance away on the outside of the tank. Fish were required to approach and bite a porthole corresponding to one of the stimuli for a food reward. Half of the fish were randomly assigned to a training schedule where stimuli became more similar as training progressed. The rest were trained only on the most difficult to distinguish version of the stimuli. All fish received a similar total amount of training regardless of the assigned schedule. We also examined whether performance on the first training trial for a given day was related to overall performance. Contrary to our hypothesis, fish in the easy-to-hard group did not perform significantly better than those in the constant-hard group. However, performance was found to be significantly higher on days when the first trial was correct compared to days on which it was incorrect, regardless of the type of training schedule. The current results contribute to understanding individual differences in perceptual learning in fish, and are consistent with research in humans, and other species, reporting better learning after initial reward.

中文翻译：

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初次试验的结果而非训练难度可预测金鱼视觉辨别力的表现。

知觉学习中的难于达到的效果表明，以更简单的例子进行训练可以促进非常相似的刺激之间最初的困难或不可能的区分。据报道在人类和其他物种中有这种作用。我们测试了难于接受的训练是否可以促进普通金鱼（Car鱼）的视觉识别。鱼（ñ = 6）执行了两种选择的强制选择判别任务，该任务包括同时在罐的外部以恒定的距离呈现两个条纹图案。鱼被要求接近并咬住与刺激之一相对应的舷窗以获得食物奖励。一半的鱼被随机分配到一个训练计划中，随着训练的进行，刺激变得越来越相似。其余的仅针对最难区分的刺激进行训练。无论分配的时间表如何，所有鱼都接受了相似的培训总量。我们还检查了一天中第一次训练试验的表现是否与整体表现有关。与我们的假设相反，易坚硬组的鱼的表现没有比恒坚组的鱼明显好。然而，不论训练时间表的类型如何，与第一次测试不正确的天数相比，发现第一次测试正确的天数的性能显着更高。目前的研究结果有助于理解鱼类在知觉学习方面的个体差异，并且与人类和其他物种的研究相一致，在获得初步奖励后报告了更好的学习。